1. Field of the Invention
The present invention relates to radio telephone systems of a multi-channel type and more particularly, to a radio telephone system which can automatically call a party telephone set at intervals of a predetermined time when the party telephone set is in its speech mode.
2. Description of the Related Art
A multi-channel type radio telephone system generally comprises a base unit connected to a wired telephone line and a radio telephone set connected to the base unit through a radio link.
With the radio telephone system having such an arrangement, when it is desired for the radio telephone set to perform communication with a party telephone set connected to an exchange which in turn leads at its another end to the other end of the wired telephone line, a caller of the radio telephone set first turns ON a hook switch provided thereon to establish the radio link between the base unit and the radio telephone set, and then enters a telephone number corresponding to the party telephone set through a dial key board provided on the radio telephone set to call the party telephone set through the base unit, the wired telephone line and the exchange. When the party telephone set answers to the call, a speech communication is established between the party telephone set and the caller radio telephone set. In this way, a speech can be realized between the radio telephone set and the party telephone set.
Meanwhile, when the party telephone set is already in its speech state and thus cannot answer to the call from the exchange, the exchange generates a busy tone (BT) and sends it to the caller radio telephone set through the wired telephone line, the base unit and the radio link. The caller or operator of the radio telephone set, when listening to the busy tone, turns OFF the hook switch to turn OFF both a transmitter of the radio telephone set and a transmitter of the base unit respectively, thus releasing the radio link established between the radio telephone set and base unit.
When the caller wants again to call the same party telephone set, the caller again turns ON the hook switch provided on the radio telephone set and then again enters the telephone number of the party telephone set through the dial keys to call the party, in the same manner as mentioned above. If the party telephone set is still in the speech mode, however, then the caller turns OFF the hook switch. After this, the same procedure must be repeated.
There has been proposed a radio telephone system of such an arrangement that the contents of the dial number entered in the previous cycle is previously stored in a control circuit of the radio telephone set or in a control circuit of the base unit so that a depression of a re-dial key provided on the radio telephone set causes sending of the same dial signal as in the previous cycle to a wired telephone line through one-touch operation. However, when the party telephone set is in the speech mode, the caller must conduct the calling operation again at the proper timing after the speech of the party telephone set is finished, requiring much labor troublesomely.
In order to avoid such troublesome operation, for example, such an arrangement is considered that, when the party telephone set does not answer to the call, the same condition as by a depression of the re-dial key of the radio telephone set is automatically established at intervals of a predetermined time to thereby automatically call the party telephone set. This arrangement is advantageous in that the troublesome calling operation at the proper timing after completion of the speech of the party telephone set can be avoided but disadvantageous in that, the radio link is established between the radio telephone set and the base unit for each calling operation, and if the call of the party telephone set fails, a waste current flows through the radio telephone set each time the call is made, which hinders the effective use of radio waves.